Electron accelerator tube



Feb. 4, 1958 R. wlDERE 2822491 ELEcTRoN AccELERAToR TUBE Filed Jan. 2, 1953 A INVENT'OR ATTORNEYS United States Patent O ELEcTRoN ACCELERATOR TUBE Rolf Widere, Ennetbaden, Switzerland, assignor to Aktiengesellschaft Brown, Boveri & Cie, Baden, Switzerland, a joint-stock company Application January 2, 1953, Serial No. 329,327

2 Claims. (Cl. 313-62) The present invention relates to electron or other charged particle accelerators of the general type popularly known as a *betatron or *synchrotron wherein streams of electrons for example are caused to be accelerated repeatedly along a closed path which is enclosed by an evacuated tube. These accelerators include a magnetic structure in which is established a magnetic field that varies in intensity with time, the field usually being produced by a winding on the structure energized from a source of alternating current. One component of the magnetic field passes through the tube at and normal to the plane of electron orbit and functions to guide and maintain the electrons on their orbit. Another component o f this magnetic field links the electron orbit and functions to accelerate the electrons through a magnetic induction effect. A typical betatron construction is shown in my U. S. Patent No. 2,586,494, issued February 19,

1952, and a typical synchrotron is shown in U. S. Patent No. '2,485,409, issued October 18, 1949, to H. C. Pollock and W. F. Westendorp.

In order to prevent formation of localzed charges on the inner wall surfaces of the tube, it has been the practice as typified by the disclosure in U. S. Patent No. 2,297,305, issued September 29, 1942, to D. W. Kerst, to provide on such surface a coating of conductive material. Since eddy currents cannot help but be induced in such coating because of the time-varied characteristic of the magnetic field the resistance of the coating must be so high as to reduce the magnitude of the eddy currents to an insignificant value.

Through operating experience, it has been found that the coating is easily susceptible to damage such as by bombardment from stray electrons which gives rise to the formation of insulated regions. Different regions may acquire different potentials when charged by stray electrons, and this has been found to interfere with the proper operation of the accelerator.

The present invention has for its objective a reduction in the harmful effect of the insulated regions which form in the conductive coating on the interior wall surface of the tube and the objective is attained by applying a conductive coating to the exterior wall surface of the tube. The capacities formed between the exterior coating and the insulated regions of the interior coating have the effect that a given charge of such a region corresponds to a much lesser potential change than Would arise if the exterior coating were lackng. The potential fields produced by such charges and the Operating disturbance of the accelerator caused thereby are like- 2',8224,'491 Patented Feb. 4, 1958 'ice wise decreased in a corresponding manner. As in the case of the inner coating, the outer coating according to the invention must be designed so as to minimize the fiow of eddy currents therein.

Fig. 1 of the accompanying drawings illustrates one practical embodiment of the invention and Fig. 2 illustrates a modified construction. It Will be noted that in both views, only the tu'be element shown in diametral section which encloses the electron orbit of the electron accelerator has been illustrated in order to simplify the drawings, it being understood that the remainder of the Operating elements can be as illustrated in either of the aforesaid referenced patents.

With reference to Fig. 1, it will be seen that the tube l, of annular configuration, and which is usually made of a dielectric material such as glass is provided with the conventional conductive coating 2 highly resistant to eddy current fiow on its interior surface. The electron path is shown by the orbit designated k. In accordance with the invention, tube 1 is also provided with the aforementioned coating 3 highly resistant to eddy current fiow on its exterior surface. This coating may consist of a material of relatively poor conductivity and can be broken up by interrupting joints 4 into mutually insulated regions kept at the same potential such as to limit the magnitude of the eddy currents induced therein.

In the modified embodiment illustrated in Fig. 2, the exterior surface coating is formed by application to the tube of a flat band 5 of poorly conducting material; such as for example constantan, wound helically upon the tube 1', the interior coating 2' being the same as in Fig. 1.

Having now described -my invention and illustrated a practical embodiment thereof, what is claimed is:

l. An annular tube providng therein an orbital path along which charged partcles such as electrons are adapted to be accelerated in a device including a timevaried magnetic field effective at the path to guide the electrons, said tube being provided on both its interior and exterior wall surfaces with equipotential coatings extending over the entire wall surfaces of the tube and presenting high resistance to the flow of eddy currents induced therein by the magnetic field, said interior and exterior coatings establishing electrical capacities therebetween for minimizing formation of localzed charges on portions of said interior coated surface which otherwise produce a disturbing effect on the travel of the electrons along the orbital path.

2. A tube as defined in claim 1, wherein said exterior coating is constituted by a band of poorly conducting material arranged in a helx about the tube.

References Cited in the file of this patent UNITED STATES PATENTS Wideroe Oct. 23, 1951 

